鈥� The primary-secondary distinction in affective disorders has been proposed to reduce the heterogeneity of depression. An investigation of the frequency of secondary depression and its nature in depressed opiate addicts, alcoholics, and schizophrenics was undertaken. Findings show that secondary depression in ambulatory patients with other psychiatric disorders is relatively common. The sociodemographic characteristics of the secondary depressives are consistent with the population from which they derive but differ from primary depressives. The symptom patterns of secondary depressives are similar to primary depressives but are overall less severe. These findings give further support to the value of separating out secondary from primary depression in future research studies.